1. Technical Field
The present invention relates to a projection lens that projects an image and the like on a screen and a projector including the projection lens.
2. Related Art
A projector that enlarges and projects an image generated by using a liquid crystal light valve, a digital micromirror device (DMD), or any other device via a projection lens on a screen has been used and is currently used. JP-A-2013-148930 discloses a projection lens (projection zoom lens) used in a projector of the kind described above. FIG. 9 is a cross-sectional configuration diagram of lens groups that form the projection lens of related art. The projection lens shown in FIG. 9 is disclosed in JP-A-2013-148930.
The projection lens disclosed in JP-A-2013-148930 has a first lens group G1, a second lens group G2, a third lens group G3, a fourth lens group G4, and a fifth lens group G5 sequentially arranged from the image magnifying side. The first lens group G1 and the second lens group G2 form a first combined lens group, and the third lens group G3 and the fourth lens group G4 form a second combined lens group. The magnification factor of a projected image is changed by changing the distance between the combined lens groups. Further the spherical aberrations, comma, and astigmatism produced when the magnification factor is changed are corrected by changing the distance between the first lens group G1 and the second lens group G2 and the distance between the third lens group G3 and the fourth lens group G4.
The projection lens disclosed in JP-A-2013-148930 includes an aperture stop 100, which controls the amount of light passing therethrough, as shown in FIG. 9. The provided aperture stop 100 controls the brightness of a projected image. Further, blocking unnecessary light rays by using the aperture stop 100 suppresses a decrease in the quality of a projected image. In the projection lens shown in FIG. 9, the aperture stop 100 is disposed in a position where the light flux diameter is minimized.
In the projection lens, the position where the light flux diameter is small is the position where illumination light converges. Providing the aperture stop 100 in the position possibly causes an increase in the temperature of the aperture stop 100. When the temperature in a member in the vicinity of the aperture stop increases, the member thermally expands, resulting in a decrease in performance of the projection lens. Further, the member heated to a high temperature, such as a lens frame, may melt, causing the projection lens to achieve no resolution. To avoid such a situation, the aperture stop 100 and the member disposed in the vicinity thereof need to be made of a heat-resistant material. For example, a metal frame, such as a part formed of a metal sheet and formed in a drawing process, is used. Use of a heat-resistant member, however, results in an increase in cost.